Reducing the risk of natural hazards in mountain resorts – Dr. David Cheer, International Rockfall Mitigation Specialist at Maccaferri, explains more

A safe mountain resort is a primary concern for the owners, operators and visitors to the resort. Notonly is this often a legal obligation, but also makes prudent financial sense. Natural hazards such asavalanches, rock falls and debris slides, unless addressed and mitigated, can be problematic to bothwinter and summer visitors.

Solutions which are more commonly used to protect civil engineering infrastructure (roads, railwaysand buildings) are increasing common within sports resorts in mountainous areas.

Depending upon the natural hazard anticipated, Maccaferri now offers a graded range of solutionsto mitigate risk from most events.

Given the safety implications of placing the rockfall barriers in the wrong location on themountainside, or the mitigation measure not performing as anticipated, resort operators arerecommended to work with an experienced solution provider. In addition, throughout the worldthere are numerous technical and product standards to which these rockfall barriers (e.g. RMCbarriers) should adhere: European Test and Approval Guideline 27 (ETAG027(1)) for rockfall fencesand CE Marking. Clients should insist upon snow supporting structures/snow nets which havecertification in accordance with the appropriate local standards. For example, a snow fence shouldbe certified by the Swiss Federal Institute for Snow and Avalanche, Davos(2), and have obtained thehomologation of the Federal Office for the Environment (BAFU-FOEN).

There are 4 zones on snow and rock slopes prone to natural hazards:

Detachment or Initiation Zone – where the avalanche breaks from the snow-pack and starts moving, or rocks detach from the slope face

Transit Zone – the hazard event is now in progress down the mountain, gaining momentum, energy and potentially size

Impact Zone– the hazard event may then impact something in its path; buildings, ski or mountain infrastructure, roads, railways or often forested areas

Within each zone, Maccaferri offers a graded range of systems of increasing capacity to provide a technically and cost efficient solution.

Solutions to minimise the risk from natural hazards can be placed in any of these zones dependingupon a sensitive balance of factors which determine the optimum solution for the location; hazardexpected, topography, geology, accessibility for installation works and cost. E.g. Snow fences orsnow umbrellas installed high in the Detachment Zone may be more technical to install thantraditional post and rail fences, but they are far less visually obtrusive, adding to the ambiance of themountain resort, especially during summer use. Also in the Detachment Zone, rockfall meshes and nets are often used on near-vertical rock faces to secure and contain unstable rocks preventing them leaving the zone, where the hazard could magnify as it gains momentum.

The use of wind-breaks on the mountain can dramatically reduce migration of snow, reducingdrifting and controlling the build-up of snow. Further down the slope, snow supporting structuresare common due to their versatility and low visual impact. In the detachment or Initiation Zone arange of high performance mesh solutions are available from Steelgrid® HR to HEA Panels and fromRing Nets to rockfall netting.

In the Transit Zone and Impact Zones, dynamic rockfall catch fences are now available fromMaccaferri with a record breaking 8,500kJ of energy absorption, equivalent to stopping a 20t trucktravelling at 67mph/hr (108km/hr) ! Maccaferri’s barriers feature compression brakes and high performance meshes to progressively deflect to dissipate the energy of a rockfall impact. The barriers have been tested in accordance with the ETAG 27 of the European Organization forTechnical Approvals (EOTA), and have been awarded an ETA for the barriers from 500kJ to 5000kJ(MEL) with a certificate pending for the 8,500kJ barrier, tested in summer 2012.

Attenuator, hybrid and DF Series debris flow barriers complete a suite of tools within theTransit/Impact Zones, available to stop the natural hazard before it damages resort infrastructure.

Debris flows, like avalanches, behave like a dense fluid and require specifically designed dynamic fences to progressively absorb the energy, slowing and ultimately stopping the flow.

Finally, in the Run-Out Zone, clients are not limited to the 8,500kJ energy absorption capacity of arockfall barrier; soil reinforcement technology can be used to create almost infinite energyabsorption capacity rockfall embankments. Reinforced with MacGrid® or Paragrid® soil reinforcementgeogrids, the embankment profile and cross sections can be tailored to suit site aesthetics and theavailable space. As Maccaferri geogrids make the ground perform better than it does in its natural state, these rockfall embankments have been constructed with modeled capacities of 20,000kJ with70’ steep faces, reducing the ‘footprint’ of the solution.

Ease of installation of the solution is always an important factor, as helicopters are often used inmountain environments. Where appropriate, solutions should be lightweight and rapid to install,minimising on-site time and costly equipment.

Regardless of the mitigation measure selected, durability and maintenance of the solution are important factors; a materially cheaper solution may actually require more expensive installation techniques or more frequent maintenance.

With the multitude of project-specific site conditions, hazards and range of solutions available in themarket, the resort operator should assemble a trusted and knowledgeable project team, to protecthis assets. In this way, natural hazard risks can be safely and cost effectively managed.(1) ETAG027 Guideline for European Technical Approval of Falling Rock Protection Kits, 2008(2) Margareth, S., 2007: Defense structures in avalanche starting zones. Federal Office for the Environment, Bern; WSL Swiss Federal Institute for Snow and Avalanche Research SLF, Davos.

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